1. Field of the Invention
The present invention relates to a light deflection device for arbitrary interconnection by light wave between desired spots. Particularly, the present invention relates to a light deflection device suitable for optical interconnection such as optical interconnection between elements in an integrated circuit, within or between apparatuses; optical switching for switch-over of transmitted optical data; and optical information processing.
2. Related Background Art
Holograms, liquid crystal switch arrays, and the like have been studied as a light deflection device for optical interconnection for programmable circuit connection. A deflection direction-variable hologram can be constituted with an optical writing type of spatial optical modulator. However, it requires interference exposure of a liquid crystal or an optical crystal, which complicates construction of the apparatus. Besides, a liquid crystal two-way switch array applicable therefor, but it requires multiple or repeated switching, complicating the apparatus, and its switching speed is lower owing to the liquid crystal properties.
Differently from the above optical deflection mechanism employing light diffraction or light refraction change, techniques are disclosed which control the light deflection by tilting a mirror according to micromechanics. For example, L. H. Hornbeck, et al. discloses a spatial optical modulator which changes the direction of reflection of an incident light beam by uniaxial turning of a thin metal plate mirror by electrostatic force (U.S. Pat. No. 5,061,049). H. Toshiyoshi, et al. discloses an optical cross connector between optical fibers by uniaxial turning of a mirror by a similar driving principle (H. Toshiyoshi, et al. "Fabrication and Operation of Electrostatic Micro Torsion Mirrors for Optical Switches", Technical Digest of 14th SENSOR SYMPOSIUM, pp.275-278, 1996). Such a thin film mirror enables miniaturization of the light deflection device and increase of the deflection angle. However, in the above devices, the light deflection direction is binarized. That is, the above device is a two-way optical switch, in which the thin film plate is moved by balance of a spring force with a magnetic force, the former varying depending linearly on spring elongation, and the latter varying depending on a reversed square of a distance, which is not suitable for fine control. Therefore, for deflection to an arbitrary direction, the device should be provided in multiplication for the switching.
Another technique employs a mirror other than the thin film plate and is disclosed in Japanese Patent Application Laid-Open No. 7-333528 in which a hemisphere having a flat face as a mirror is placed in a concave filled with an optical oil, and the hemisphere is turned by a non-contacting or contacting driving mechanism placed in opposition to the flat face. This device is capable of deflecting an incident light beam to an arbitrary direction by turning the hemisphere body, rendering multi-switching unnecessary.
With the above light deflection device, to stop the hemisphere body being turned by the torque exerting to the flat face of the hemisphere body at a desired position as shown in FIG. 1A, the same strength of torque as that for the turning direction should be applied in the reverse direction. If the torque (F1.times.r1) for the turning movement is not equal to the torque (F2.times.r2) for stopping the turning movement, the hemisphere body 81 will turn to the resultant torque direction. The total resultant torque should be zero to stop the turning. Further, in a freely turnable hemisphere body, the positions of the torque application points (r1, r2) are not fixed, but shift to positions (r1+.delta.1, r2+.delta.2) depending on the turning angle .theta. as shown in FIG. 1B.
Practically, in this contact type driving mechanism of this light deflection device, the turning movement of the hemisphere body may be stopped by pressing the flat face portion against the concave without application of a stopping torque independently of the position of the action point. However, in this operation, excessively strong force is applied to the contact points on the flat face, and the contact point between the hemisphere and the concave tends to cause plastic deformation of the hemisphere and the concave and to lower the durability of the light deflection device. Further, the contact type of driving mechanism requires a movable element such as an electromagnetic actuator, complicating the apparatus and inhibiting miniaturization of the apparatus and device arraying. Furthermore, such a driving mechanism having the movable element is not readily sealed tightly to prevent leakage of the optical oil from the concave.
On the other hand, a non-contact type driving mechanism is advantageous in miniaturization and arraying of the device, and can readily enclose the optical oil by eliminating the movable element. However, in the non-contact type driving mechanism, the forces (F1, F2) and the force application points (r1, r2) both vary depending on the tilting angle of the hemisphere body, since the forces (F1, F2) such as electrostatic forces and magnetic forces depend on the distance from the flat face of the hemisphere and the force application points (r1, r2) shift thereby. Therefore, the tilting angle of the hemisphere is not readily controllable. However, it has the aforementioned advantages. In consideration of the torque control for stopping the turning movement of the hemisphere, the non-contact type driving mechanism has difficulty in torque control disadvantageously owing to many parameters involved, since the forces (F1, F2) such as electrostatic forces and magnetic forces depend on the distance from the flat face of the hemisphere, or the tilt angle of the hemisphere, and the force application points (r1, r2) also depend on the tilt angle as shown in FIGS. 1A and 1B.
A non-contact type driving mechanism as shown in FIG. 2A is disclosed in Japanese Patent Application Laid-Open No. 7-333528. In this constitution, hemisphere body 91 is supported only by contact portion of a conical pit. Therefore, when the attitude of the light deflection device is changed, for example reversed upside down as shown in FIG. 2B, the hemisphere is not supported. Thus, the attitude of the device is naturally limited to be controllable. In FIGS. 2A and 2B, the numeral 92 indicates flat face portion; 93, a supporting member; 96 and 102, driving electrodes respectively; 100, supporting base plate; and 103, a spacer.
In the above constitution disclosed in Japanese Patent Application Laid-Open No. 7-333528, the turning center R and the gravity center G of the hemisphere as a turning body are apart at a distance r3 as shown in FIGS. 3A and 3B. Therefore, with hemisphere body 91 and an optical oil having specific gravities different from each other, the resultant force Fg derived from gravity and buoyancy at the gravity center acts as a turning torque (Fg.times.r3) disadvantageously. The turning torque of the resultant force at the gravity center remains after the hemisphere has been turned by the driving mechanism to a desired position. To keep the hemisphere body at the desired position, any of the following measures should be taken: (1) a compensation torque is kept applied, (2) the static friction coefficient is increased at the contact point with the concave, and (3) the resultant force from the buoyancy and the gravity is adjusted to be zero (that is, the specific gravities of the hemisphere body and the lubricating liquid are equalized).
The above measure (1) complicates greatly the control system in an array construction of the light deflection device. The above measure (2), although effective and practicable, is not compatible basically with the lubricity, tending to render insufficient the turn movement control and to cause deterioration of the parts by friction, and moreover, rendering the friction force ineffective in a certain attitude of the light deflection device. The above measure (3) is limited in reducing the specific gravity of the hemisphere body, and selection of the construction material especially when the refractive indexes of the optical oil and the hemisphere body are required to be equal in addition to the requirement for the specific gravity.